Travellers who want to swim with migrating whale sharks near Cancun are often told by tour operators that only biodegradable sunscreen is permitted.

And those visiting the nearby Mayan-themed
nature parks Xcaret and Xel-Ha face similar rules, lest travellers
leave behind an oily trail when they snorkel or swim with dolphins. In its 2011 annual report, Xcaret said that its parks handed
out 152,506 samples of “chemical-free” sunscreen and invested 354,238 pesos in the program.

So should ocean-bound vacationers pack only the
biodegradable stuff? Travellers certainly can do that, but experts say
sunscreen is not a big contributor to the destruction of reefs worldwide.

A 2008 study published in the US-based Environmental Health Perspectives
journal in the US found that the ultraviolet filters in sunscreens bleach hard
corals by causing a viral infection in the algae that keep coral healthy. The
authors concluded that sunscreens “potentially play an important role in coral
bleaching in areas prone to high levels of recreational use by humans”. And
they estimated that about one quarter of the sunscreen tourists apply washes
off when they swim or bathe, “accounting for a potential release of 4,000 to 6,000
tons per year in reef areas”.

In the June
issue of Vancouver-based Diver magazine, Jean-Michel Cousteau, son of
Jacques Cousteau and founder of the marine conservation group Ocean Futures Society, promoted the use of biodegradable
products, saying that ingredients including zinc oxide and titanium dioxide
“will never biodegrade and have the potential to harm corals and sea life”. Cousteau
wrote that he “would not suggest that sunscreen products are the primary reason
our reefs are collapsing”, but “everything is connected”.

Choice of sun block, however, doesn’t register
as an issue with Carl Safina, founding president of the conservation group Blue Ocean Institute at Stony Brook University
in New York. “I think that it would be a trivial thing compared to other
things, such as the overfishing that afflicts almost all of the reefs of the
world, the pollution from nearby towns, the warming of the water which
certainly triggers bleaching over very large areas, and the acidification of
the ocean that is also resulting from the same carbon dioxide that is causing [the
water’s] warming.”

Kiho Kim, professor of environmental science at Washington DC’s American University, specialises in coral
reef ecology. He, too, said that while it’s good to use products that are
biodegradable, the issue with sunscreen is “probably not even on the radar of
things people ought to be thinking about”. According to Kim, pollution is one
of the primary concerns on the local level. Many places in the tropics, he
said, “don’t have the level of water treatment that would relieve the coral reefs
from much of the pressure from water pollution”.

The Coral
Reef Alliance, based in San Francisco, lists several things people
can do to help protect coral reefs: choosing sustainably-harvested seafood and
not buying coral jewellery are a few. But using biodegradable sunscreen isn’t
one of them. "It’s not the thing that we feel is really going to be the
turning point," said conservation programs director Rick MacPherson. If
the topic of sunscreen launches a conversation on other threats and action
people can take, he said, that’s great. But “when we focus too much on
something like the sunscreen, that makes it feel like it’s one and done”.

Kim said concerned travellers should ask what steps their hotels are
taking to treat wastewater and think about how much carbon they’re emitting by
flying to their holiday destination. Both Kim and Cousteau cautioned against
“green washing” -- whether it’s tour operators promoting biodegradable
sunscreen but doing little else environmentally, or sunscreen companies falsely
touting products as eco-friendly.

“Travelling is not particularly
sustainable,” Kim noted. And there’s only so much people can do to lessen that
impact. “If biodegradable sunscreen is part of the mix”, he said, “that’s
fine.” But travellers “shouldn’t have the illusion that [they’re] protecting
the destruction of the coral”.